1. Field of the Invention
The invention generally relates to ophthalmic lenses and, more particularly, the invention relates to ophthalmic lenses for increasing the depth of focus of the human eye.
2. Description of the Related Art
It is well-known that the depth of focus of the human eye can be increased with the use of ophthalmic lenses with pinhole-like apertures substantially near the optical center of the lens. For example, U.S. Pat. No. 4,976,732 (“the '732 patent”) discloses an ophthalmic lens with a pinhole-like aperture. In the '732 patent, a mask forms the pinhole-like aperture. In one embodiment, the mask is circular in shape. When the pupil is constricted, light enters the retina through the pinhole-like aperture. When the pupil is dilated, light enters the retina through the pinhole-like aperture and the outer edges of the mask.
In addition, U.S. Pat. No. 3,794,414 (“the '414 patent”) discloses a contact lens with a pinhole-like aperture. In the '414 patent, the mask forming the pinhole-like aperture has radial slits and/or scalloped edges. In addition, the mask forming the pinhole-like aperture is two spaced-apart concentric circles. However, the radial slits, scalloped edges and two spaced-apart concentric circles promote light diffraction, which in turn reduces the contrast of the image.
In U.S. Pat. Nos. 4,955,904, 5,245,367, 5,757,458 and 5,786,883, various modifications to an ophthalmic lens with a pinhole-like aperture are disclosed. For example, the patents disclose use of an optical power for vision correction in the pinhole-like aperture, or use of an optical power for vision correction in the area outside the mask. In contrast, in U.S. Pat. No. 5,980,040, the mask is powered. In particular, the mask is powered to bend the light passing through the mask to impinge on the retina at a radial distance outside of the fovea. In other words, the mask is powered to “defocus” the light.
In each of these patents, the mask forming the pinhole-like aperture is made, in whole or in part, of a light absorptive material. A light-absorptive material is a material in which light is lost as it passes through the material, generally due to conversion of the light into another form of energy, e.g., heat.